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2.2.3Force and Translational Dynamics

Net Force — AP PHYSICS 1 Revision Notes & Topical Questions

5 min read 8 parts Lesson 8 of 36 1 quiz

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Lesson summary

2.2.3 Net Force — AP PHYSICS 1 notes: Define net force as the vector sum of forces and distinguish balanced from unbalanced forces.Net force — the vector sum of all forces exerted on a system; also called the resultant forceWhat it determines — whether the speed or direction of m…

  • Self-forces
  • Different directions
  • Perpendicular
  • What it determines — whether the speed or direction of motion changes
  • Draw the free-body diagram
  • Choose a positive direction for each axis

Part 1 of 6Net force

Net force
  • Net force the vector sum of all forces exerted on a system; also called the resultant force
What it determines
  • What it determines whether the speed or direction of motion changes
Self-forces
  • Self-forces a system cannot exert a net force on itself

Part 2 of 6Balanced and unbalanced forces

TypeNet forceEffect
BalancedZeroSystem in translational equilibrium; velocity constant
UnbalancedNon-zeroSystem accelerates in the direction of the net force

Part 3 of 6Finding the net force

1
Draw the free-body diagram.
2
Choose a positive direction for each axis.
3
Add the force components along each axis with their signs.
4
Combine the axis totals with Pythagoras and trigonometry if needed.

Part 4 of 6Pattern: tug-of-war

Forces
  • Forces person A pulls 80 N left and person B pulls 100 N right
Resultant
  • 20 N to the right, so the rope is unbalanced

Part 5 of 6Directions

Same line
  • Same line net force is the signed sum
Different directions
  • Different directions use components and add vectors tip to tail

Part 6 of 6More from the specification

More from the specification
Resultant net force down an inclined slope
  • Resultant net force down an inclined slope resolving component forces of interacting lattice atoms determines net acceleration down an inclined plane slope.
Coordinate system
  • Perpendicular axes used to resolve forces.
Inclined plane
  • Flat surface tilted at an angle.
Reaction force
  • Force from a support pushing up on an object.
Force triangle
  • Closed tip-to-tail vector triangle of balanced forces.
Normal
  • Line at 90° to a surface.
Perpendicular
  • At right angles.
Electron
  • Negatively charged particle in an atom.
Weight
  • Gravitational force on a mass.
Parallel
  • Components on separate branches, each with the full e.m.f.
Stationary
  • Not moving.
Thrust
  • Force produced by an engine.
Upthrust
  • Upward force exerted by a fluid.

Key terms

TermMeaning
Net forceVector sum of all forces on a system.
Resultant forceAnother name for net force.
Balanced forcesForces with zero net force.
Unbalanced forcesForces with a non-zero net force.

Avoid these mistakes

Avoid these mistakes
Adding magnitudes of forces that act in different directions.
Thinking the largest force is always the net force.
Including a force the object exerts on something else.

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